The present invention relates to light emitting elements of a semiconductor, in particular, to an electrode structure of the light emitting element.
The light emitting element using a nitride semiconductor emits light in near-ultraviolet ray to red region due to the wide band gap characteristics thereof, and thus various researches are being carried out. A general basic structure of the nitride semiconductor light emitting element has a structure in which an n-type nitride semiconductor, an active layer, a p-type nitride semiconductor are stacked on a substrate, where each electrode is arranged in a p-layer and a partially exposed n-type layer, and research is being carried out on the light emitting structure including the electrode structure. In particular, various light emitting structures as well as electrode structures are being proposed in an aim of achieving high output.
Conventional proposals include,
(1) using a transparent electrode such as ITO for the p electrode arranged on the light emitting structure, arranging a current blocking part of an insulating film at one part, and selectively light emitting the transparent electrode part as disclosed JP-H08-250769A, JP-H09-129921A, WO98-42030A, JP-H10-173224A;
(2) other structure for separating an external connecting part and a light emitting part as disclosed in JP-2003-124517A; and
(3) a structure of arranging and overlapping a metal layer/reflection layer partially on the upper layer such as in JP-2003-124517A, or entirely on the upper layer such as in JP-2005-197289A, JP-2004-179347A, JP-2005-317931A for an electrode double-layer structure of n electrode and the like.
According to the conventional structure, in the structure of retrieving light in a region of transparent electrode, in particular, the sheet resistance of such electrode becomes high, where in such structure, an element resistance becomes high when adding a structure of selective light emitting/partial current blocking part, and light loss in a selective light emitting/current injecting part tends to increase, and furthermore, wall-plug efficiency (W.P.E) tends to lower. In application and general use to illumination application etc. of the semiconductor light emitting element, enhancement in high mass productivity, lower cost, light output, and power efficiency becomes necessary. In particular, power efficiency is sometimes a difficult demand since the element resistance such as Vf needs to be reduced, and light emitting characteristics and light retrieving efficiency must be enhanced.
In a conventional proposal from a different standpoint, the n electrode arranged in the n-type layer includes,
(1) using a transparent electrode such as ITO as disclosed in JP-2003-060236A, JP-2005-317931A; and
(2) a structure of overlapping and arranging a metal layer/reflection layer partially or entirely on the upper surface as disclosed in JP-2001-102631A, JP-2003-133590A, JP-2004-179347A, and JP-2005-317931.
Another further proposal includes suppressing the light shielding effect by lowering the height of the n electrode in JP-2001-102631A, enhancing the reflection effect by inclining the side surface of the n electrode in JP-2004-128321A, and the like with respect to the light emission from the active layer.
Here, the notation JP-[number]A refers to the Japanese Laid-Open Patent Publication number, and the notation WO[number]A refers to the International Publication number.